Semiconductor devices are commonly found in modern electronic products. Semiconductor devices vary in the number and density of electrical components. Discrete semiconductor devices generally contain one type of electrical component, e.g., a light emitting diode (LED), small signal transistor, resistor, capacitor, inductor, or power metal-oxide-semiconductor field-effect transistor (MOSFET). Integrated semiconductor devices typically contain hundreds to millions of electrical components. Examples of integrated semiconductor devices include microcontrollers, microprocessors, charged-coupled devices (CCDs), solar cells, and digital micro-mirror devices (DMDs).
Semiconductor devices perform a wide range of functions such as signal processing, high-speed calculations, transmitting and receiving electromagnetic signals, controlling electronic devices, transforming sunlight to electricity, and creating visual projections for television displays. Semiconductor devices are found in the fields of entertainment, communications, power conversion, networks, computers, and consumer products. Semiconductor devices are also found in military applications, aviation, automotive, industrial controllers, and office equipment.
Transient-voltage-suppression (TVS) diodes are commonly used to protect semiconductor devices from electrostatic discharge (ESD). A TVS diode can be coupled in parallel with a load to shunt transient voltage spikes away from the load, typically to ground. FIG. 1 illustrates one example with regard to a mobile device 10 having a Universal Serial Bus (USB) port 12. A data line 14a and ground line 14b are routed on a printed circuit board (PCB) from USB port 12 to a microprocessor (CPU), USB controller, or other semiconductor device 16. Data line 14a allows high-speed transfer of data between CPU 16 and an external device connected to USB port 12. A ground line 14b is routed from USB port 12 to CPU 16 so that the external device and mobile device 10 are operating on the same ground voltage potential.
TVS diode 20 is coupled from data line 14a to ground line 14b to protect CPU 16 from electrical overstress (EOS) and ESD events on data line 14a. TVS diode 20 is approximately an open circuit at normal voltage levels for data line 14a. However, the resistance of electrical current through TVS diode 20 is substantially reduced when the voltage potential of data line 14a increases over a breakdown voltage of the TVS diode. Excess electrical current from ESD or EOS events on data line 14a flows through TVS diode 20 to ground line 14b, which helps keep the voltage potential at data line 14a within safe levels for the interconnect terminal of CPU 16.
One problem with TVS diodes for ESD and EOS suppression is that TVS diodes have a junction capacitance that is proportional to the current handling capability of the TVS diode. When used to protect high-speed data lines, a low capacitance is generally desired to reduce adverse effects of the junction capacitance on signal integrity. One method of reducing apparent capacitance of the TVS device is to integrate steering diodes in a bridge configuration. A TVS device including steering diodes has a reduced capacitance, allowing the TVS device to be better suited for high frequency data lines, but then the TVS device is of limited use for EOS protection due to lower current handling capability. Low capacitance to ground and high current surge capability remain difficult to achieve together.